Structure of an absorption column

ABSTRACT

A column structure is described for the containment of high surface area packing and absorbent liquid reagent for the removal of a target gas from a gas stream. The column structure comprises at least one vessel having an elongate upright wall structure to define an absorption process volume for the containment of high surface area packing and for the countercurrent flow of absorbent liquid reagent and target gas in use; and a column perimeter structure comprising an elongate upright wall structure disposed around the at least one vessel in such manner that an inner wall of the elongate upright wall structure and an outer wall of a vessel cooperably define and fluidly enclose at least one secondary fluid volume fluidly isolated from the absorption process volume(s). A method of assembly of such a column and to a method of removal of a target gas from a gas phase using such a column are also described.

The invention relates to a column structure for an absorption columncomprising a containment vessel and structured packing for use with anabsorbent liquid reagent to effect the removal of a target gas from agas phase. The invention relates in particular to a column structure fora packed tower absorber column for removing CO₂ from a gas phase bymeans of absorption. The invention is particularly suitable for use inremoving CO₂ from the flue gases of thermal power plants fired bycarbonaceous fossil fuels, both as new build and for retrofitting intoexisting thermal power plants. The invention also relates to a method ofassembly of a column and to a method of removal of a target gas from agas phase using such a column.

Most of the energy used in the world today is derived from thecombustion of fossil fuels, such as coal, oil, and natural gas.Post-combustion carbon capture (PCCC) is a means of mitigating theeffects of fossil fuel combustion emissions by capturing CO₂ from largesources of emission such as thermal power plants which use fossil fuelcombustion as the power source. The CO₂ is not vented to atmosphereremoved from flue gases by a suitable absorber and stored away from theatmosphere. Other industrial processes where similar principles might beapplicable to capture post-process CO₂ might include removal of CO₂generated in a process cycle, for example removal of CO₂ from theprocess flow during production of ammonia, removal of CO₂ from a naturalgas supply etc.

It is known that CO₂ can be separated from a gas phase, for examplebeing the flue gas of a thermal power plant, by means of absorption bypassing the gas through a column where the gas flows in an oppositedirection to an absorbent in liquid phase. Such a process is sometimesreferred to as wet scrubbing. A well known absorbent reagent comprisesone or more amines in water.

Packed tower absorber column technology is well established to exploitthis. An absorption plant consists of at least one column where liquidabsorber is run through the column as the gas that is to be scrubbed ispassed in the other direction. The column is usually vertical and thegas introduced into the lower part of the column and fresh absorbentsolution is introduced from the top of the column.

Typical columns consist of multiple sections of structured packingconsisting of multiple thin plates or like structures to maximize thesurface area for mass transfer. These are stacked within a containmentvessel of steel or other suitable structural material. The primaryloading consideration is that attributable to the weight of the columnwhich is supported directly by the external walls of the vessel.

As used herein, the term absorption column means an elongate structurecomprising an outer vessel wherein liquid and gas phases arecountercurrently brought into contact to effect separation of acomponent of the gas phase into an actively absorbent component of theliquid phase.

The term column section is generally used to mean a zone within a columnfilling the column to its transverse extent, and being defined at thetop or bottom by liquid and/or gas distributors respectively, and willtypically comprise a support means for a section of packing.

The term packing refers generally to bodies of appropriate size, shapeand configuration for fitment into the column to provide a high surfacearea volume density for the absorbent liquid to allow high mass transferrates at the liquid-gas interface during countercurrent flow. Althoughrandom packing structures are known, where individual packing unitsand/or the surface elements thereof are not in a particular packingorientation, the invention particularly relates to structured packing,where individual units and the surface elements thereof have specificorientation relative to each other and, in the stacked state, relativeto the columnar direction. Typical structured packings for absorbentcolumns for the absorption of flue gases such CO₂ are made of thin metalfoil, expanded metal or woven wire screen stacked in layers. Polymericmaterial structures are also used in some cases. Thin steel foilstructures are particularly preferred.

The gas volumes involved in post-combustion carbon capture at full scalefrom large thermal power plants burning carbonaceous fossil fuels are ona scale out of proportion with other industries. Full scale operationmight require up to 20,000 t CO₂ or more to be captured per day (1000t/hr). This presents serious upscaling issues. Packed Bed absorbertowers which are capable of absorbing 700 t CO₂ per hour or more willpresent challenges of scale, design, construction and operation. Asingle column for a 350 MW system based on existing packing andabsorbing structures and a height of 60-80 m might be required to be 18m diameter. A single column for an 800 MW system based on existingpacking and absorbing structures might require to be 24 m diameter.

However, the scaling up of column designs presents new challenges. Theloadings on the column increase. Shipping issues also arise. The cost ofshipping anything above 6 m diameter is significant. However, a 6 mcolumn is able to handle a maximum of about 100 tonnes CO₂ per day.

Current technology for the absorber internal packing design and themethod of erection of a column with structured packing involves theproduction of blocks of structured packing which are then erected onsite. Each block tends to occupy a volume of 0.17 m³.

There are approximately 78, 500 such blocks of packing required for acolumn for an 800 MW system. Such volume requirements mean that theconventional method of packing may not be cost effective on the scalerequired for post-combustion CO₂ capture, where cost reduction is asignificant driver.

There is thus considerable incentive to develop alternative designs andmethods of column assembly and packing assembly that are practical on alarge scale.

In particular, considerations arise because of the absorption processchemistry. The absorption process typically involves a harsh chemicalenvironment within the active volume. Large column structures result inlarge mechanical loads. The concurrent requirements for materials thatoptimize mechanical strength and materials that optimize chemicalresistance can produce complex composite structures and/or structuresthat are compromises between the two requirements.

In accordance with the invention in a first aspect there is provided acolumn structure for the containment of high surface area packing andabsorbent liquid reagent for the removal of a target gas from a gasstream comprising:

at least one vessel having an elongate upright wall structure to defineand fluidly enclose an absorption process volume for the containment ofhigh surface area packing and for the countercurrent flow of absorbentliquid reagent and target gas in use;

a column perimeter structure comprising an elongate upright wallstructure having a continuous and closed perimeter disposed around theat least one vessel in such manner that an inner wall of the elongateupright wall structure and an outer wall of a vessel cooperably defineand fluidly enclose at least one secondary fluid volume fluidly isolatedfrom the absorption process volume(s).

The at least one vessel thus defines a fluidly enclosed absorptionprocess volume for the countercurrent flow of absorbent liquid reagentand target gas in use in that an inner wall of the vessel fluidlyencloses an absorption process volume. Plural vessel modules may be usedto make up a modular vessel. The column perimeter structuresurroundingly encloses the volume containing the at least one vessel andforms a continuous closed outer wall. The column perimeter structurethereby encloses at least one secondary gas volume. The secondary gasvolume is defined at least within the space between an inner wall of theelongate upright wall structure and an outer wall of each at least onevessel. In the case of a plural modular vessel arrangement the secondarygas volume may additionally include spaces between outer walls of eachvessel module.

The at least one secondary volume is arranged such as to be fluidlyisolated from the at least one absorption process volume. For example,an absorption process volume may be provided with spaced inlet andoutlet means (such as an inlet towards one end and an outlet towardsanother end) to effect in use the countercurrent flow of absorbentliquid reagent and target gas, and the at least one secondary volume maybe sealingly isolated therefrom.

This arrangement confers a particular possible operational advantage inrelation to the perimeter structure. The chemical atmosphere within eachprocess volume is likely to be harsh. A vessel or vessel module requiresappropriate material selection and structure to accommodate this harshchemical environment. However, the perimeter structure is primarilyintended to be a mechanical support structure. Defining one or moresecondary fluid volumes in the way envisaged means that the perimetersupport structure is exposed only to the fluid environment in thatsecondary volume. The fluid environment in the secondary volume need notbe chemically harsh, as the secondary volume does not define anabsorption volume. The secondary volume may be relatively inert. Atleast, the secondary volume need not be supplied with absorbent liquidreagent.

The process volume defined by a vessel or by the vessel modules as thecase may be is thus kept fluidly separate from any secondary volumedefined as part of the assembly but outside the process volume definedby each vessel or vessel module. Such a secondary volume for examplecomprises a space between the wall(s) of a vessel module and eachadjacent module and/or a space between the wall(s) of a vessel or vesselmodule and the perimeter structure.

Such spaces are adapted to define one or more secondary fluid volumesfluidly distinct from the active primary absorption volume made up bythe process volume(s) defined by the vessel(s). The spaces betweenadjacent walls of each vessel module, and/or the spaces between walls ofa vessel or vessel module or vessel assembly and the perimeterstructure, are fluidly isolated from the process volumes defined by thevessel(s) and form one or more such secondary fluid volumes. In apossible case, one or more such secondary fluid volumes are defined atleast by the outer wall surface(s) of the wall(s) of the vessel(s) orvessel modules which form the perimeter of the vessel structure and theinner wall surface(s) of the perimeter structure itself. In such a case,the perimeter structure preferably forms in combination with the outerwall surface(s) of the wall(s) of the vessel(s) a continuous elongateenclosure, and is at least to the extent necessary to do this acontinuous and fluidly closed wall structure.

The assembled column may further comprise fluid seals appropriatelylocated in the spaces between the said walls to fluidly separate theprocess volume(s) from the secondary volume(s).

Thus a vessel or an assembly of vessels is and/or vessel modules are soarranged that the primary absorption volume is fluidly separate from oneor more secondary fluid volumes. Means are preferably provided to supplyabsorbent liquid reagent only to the active primary absorption volume,to supply gas to be processed to the process volumes to flowcounter-currently with the absorbent liquid reagent, and to supply gasto the secondary volumes to create a relatively less chemically reactiveatmosphere, in particular being an atmosphere with at least much reducedlevels of absorbent liquid reagent. The gas so supplied may simply bedry gas to be processed (ie the gas for processing without absorbentliquid reagent present), or may be another relatively inert gas. Thesupply means may be adapted to supply the gas to the secondary volumebefore supply of the liquid reagent to the primary active volume and/orat a slight over-pressure to prevent leakage of wet gas (that is, gascarrying absorbent liquid reagent) from the primary active volume. Aparticular advantage of this arrangement is that it entirely isolatesthe perimeter structure from the harsh environment within the activevolume. The perimeter structure can be optimized for its mechanicalsupport role, and need not be provided with chemical resistance. Thewall(s) of the vessel(s) defining process volume(s) making up the activeprimary volume are optimized for chemical resistance, but need not havea major structural role.

The column perimeter structure describes an outer perimeter for thecolumn volume, which surrounds the column volume in closed manner, forexample defining a perimeter comprising a closed simple polygon orclosed simple curve, in which one or more vessels are disposed. Theprocess volume(s) within the vessel(s) collectively comprise a primaryactive absorption volume for the containment of high surface areapacking and for the countercurrent flow of absorbent liquid reagent andtarget gas in use. The column perimeter structure comprises a secondarywall structure surrounding the active volume and defining a secondaryvolume.

Thus, the column defines a tower suitable for use as a packed tower fora wet scrubbing process of a gas phase in familiar manner. It isdistinctly characterised by the provision of a column perimeterstructure comprising a secondary wall structure surrounding the processvessel(s) provided for the wet scrubbing process but structurallydiscrete and fluidly isolated from the vessel wall(s) of the processvessel(s). This allows the column perimeter structure to be fabricatedwith its structural role in mind, without concerns over the harsh fluidenvironment of the process volume(s).

The column perimeter structure may be similarly shaped to the perimetersurface of the active volume process defined by the process vessel(s)and concentrically disposed with respect to the active volume but thisis not a necessary condition.

Each vessel defines a process volume for the containment of high surfacearea packing and absorbent liquid reagent for the removal of the targetgas from the gas stream. However, the perimeter structure contributes tothe overall structural integrity of the column, and in particular in apreferred case carries a substantial part of the structural load of thecolumn structure, and more preferably most of the load of the columnstructure. That is, in the preferred case the at least one vessel andthe elongate upright wall structure are mechanically arranged in suchassembled manner that a major part of the load of the assembled columnstructure is carried by the column perimeter structure.

As has been noted, an advantage of such an arrangement is that thevessel walls making up the active volume and the walls of the perimeterstructure may focus on different principal roles for which they arerespectively optimized. The vessel walls of the active volume define areaction volume for the absorption process. The absorption processtypically involves a harsh chemical environment within the activevolume.

Large column structures result in large mechanical loads. In the abovedescribed arrangement, the outer perimeter structure is not necessarilyexposed to such a harsh environment, which is contained entirely withinthe walls of the vessel(s) making up the active volume. Accordingly, itneed not be optimized for chemical resistance, and can instead beoptimized for mechanical strength. Conversely, if the column structureis adapted such that the perimeter wall structure is the substantialprimary load bearing structure, and in particular is adapted in suchmanner as to carry the weight of the vessel(s) within it and/or thestructured packing within the vessel(s), the mechanical strengthrequirements for the vessel walls can be reduced and they can instead beoptimized for chemical resistance.

The perimeter wall structure may additionally comprise a roof closure orpartial closure. The roof closure or partial closure and/or additionalmeans disposed and supported within a roof volume it defines may beadapted to contribute to a column load bearing capacity of the perimeterwall structure.

The perimeter wall structure defines a secondary fluid enclosure volumeat least in part in conjunction with the outer wall(s) of the vessel(s)that it surrounds. Optionally, any vessel wall adapted in use to sitadjacent to an inner wall of the perimeter structure is arranged toextend substantially parallel to the adjacent portion of the inner wallof the perimeter structure.

The invention is applicable to a column design in which a plurality ofcolumn sections each comprising a separate packing layer is provided insuccession vertically. Preferably in such case, a plurality of columnsections comprising each separate packing layer is provided inaccordance with the foregoing.

In a possible embodiment the column structure comprises a plurality ofvessel column modules each having an elongate upright wall structure,the column modules being adapted to be disposed together alongside oneanother in two dimensional array to constitute collectively a columnarvessel assembly.

In a possible embodiment each column module may comprise a plurality ofvertically disposed sub-modules. This is intended to facilitatepre-fabrication and assembly in situ, in particular to facilitateassembly with a loading arrangement whereby at least a substantial partof the structural load of the column structure is carried from the topvia the upper column support structure.

A sub-module may comprise a basket. A basket in this context comprises asupport structure for a discrete portion of high surface area packingmaterial. A basket comprises at least a horizontal support surfaceadapted to carry a discrete portion of high surface area packingmaterial. A basket optionally comprises additional wall structures.

A vessel or vessel module has an elongate upright wall structuredefining a perimeter that surrounds a process volume within the vessel,said perimeter for example comprising a closed structure such as aclosed simple polygon or closed simple curve or combination. That is,the elongate upright wall structure may comprise a plurality of planarwalls defining straight edges of a polygonal perimeter or part thereofand/or one or more curved walls defining arcuate edge(s) of a curvedperimeter. The walls extend in elongate manner such that a vessel orvessel module may have a (partly) prismatic and/or (partly) cylindricalstructure.

Where plural vessel modules are used these are typically arranged in twodimensional array to extend generally vertically in generally parallelmanner. The vessel modules thus collectively comprise a columnar vesselassembly. Although the modules may define fluidly separate processvolumes for the containment of high surface area packing and for thecountercurrent flow of absorbent liquid reagent and target gas, themodule volumes collectively comprise an active absorption volume and themodules at least to that extent collectively comprise a single columnstructure. The active absorption volume collectively so defined is usedfor the removal of a target gas from a gas stream by means of anabsorbent liquid reagent, and the packing layer provides a high surfacearea for mass transport.

Preferably, plural vessel modules are arranged in such manner thatadjacent vessel walls of adjacent vessel modules extend substantiallyparallel to one another when the vessel modules are located in position.Adjacent vessel walls of adjacent vessel modules may abut or may bespaced apart. Spaces between adjacent vessel walls of adjacent vesselmodules may form part of a secondary volume as above defined.Conveniently, the vessel walls are generally evenly spaced when thevessel modules are located in position.

Conveniently, plural vessel modules are located in a regular arrayextending in two dimensions, for example, a square, rectangular orhexagonal array, for example essentially in tessellating manner.

The module volumes of the modules making up a vessel assemblycollectively comprise an active volume for the containment of highsurface area packing and absorbent liquid reagent and in which theabsorption process takes place. The walls or parts thereof of eachvessel module lying on the periphery of the vessel assembly define aperimeter surface and perimeter shape of the vessel assembly and of theactive volume and therefore comprise one or more perimeter walls orparts thereof of such a perimeter surface of the active volume. Suchwalls are suitably shaped with this purpose in mind.

In a convenient arrangement of modular vessel assembly a polygonal shapeis preferred for at least some vessel modules. That is, such a vesselmodule comprises an elongate prismatic vessel having plural planargenerally vertical walls together defining a closed simple polygonalperimeter.

In a preferred case of modular vessel assembly, all vessel module wallsthat are internal to the vessel assembly when assembled, that is allwalls of a vessel module adapted to sit adjacent to the wall of anothervessel module, are planar.

Optionally, perimeter walls forming in a vessel assembly of pluralvessel modules a part of the perimeter of the vessel assembly, and whereapplicable thus seating adjacent to an inner wall of the perimeterstructure, may be of different shape, for example curved, to define acurved perimeter to the vessel assembly and/or to sit complementarilywith a curved inner wall of a perimeter structure.

In a convenient embodiment of modular vessel assembly, all vesselmodules adapted to sit entirely internally in a vessel assembly, whichis to say having no wall making up any part of the perimeter of thevessel assembly when assembled, have a square or rectangular perimetershape. Conveniently, all entirely internal vessel modules are ofidentical shape and size. Vessel modules which sit peripherally in thevessel assembly such that at least one wall or part thereof of such avessel module forms a part of the perimeter of the vessel assembly maybe irregular polygons or have one or more curved walls to accommodate aparticular desired perimeter shape. However, it is desirable for ease ofassembly that the number of different shapes of vessel module isminimized.

Preferably the perimeter structure comprises a vessel having an elongateupright wall structure for example defining a perimeter comprising aclosed simple polygon or closed simple curve.

Preferably the perimeter structure comprises a primary load bearingstructure by means of which the load attributable to the weight ofvessel and/or columnar and/or packing structures is transmitted to theground.

For example the perimeter structure includes or mechanically supports acolumn top support structure located in the vicinity of the upper partof a column structure so assembled; and a vessel and where applicableeach column module is mechanically supported from the column top supportstructure.

Additionally or alternatively for example, one or more transverseplatform supports may be provided extending within the walls of a vesselto provide a support structure for a high surface area packing material.In a preferred case the perimeter structure is adapted to provide a loadbearing structure by means of which the load attributable to the weightof the platform and packing structures thereon is transmitted to theground.

In a possible embodiment of load bearing structure a column perimeterstructure is provided with:

a top support structure extending inwardly from the perimeter of avessel towards the top thereof; and

slung tensile members attached to the top support structure andextending downwardly to support at least one internal column structure.

Such an internal column structure may include a transverse platformsupport structure for a high surface area packing material, a vessel ora vessel module. Thus, the perimeter structure carries at least in partthe load for a support structure for a high surface area packingmaterial and/or a vessel and/or a vessel module via the slung tensilemembers and through the top support structure into the perimeterwall(s).

The top support structure may be integral with a roof closure or partialclosure of a perimeter structure, for example integral with a roofclosure or partial closure defining a wall structure sloping in taperedmanner upwardly towards the centre (for example comprising an optionallyfrusticated dome, ogive or pyramid). Additionally or alternatively thetop support structure may be separately provided as a bespoke supportstructure towards the top of the column for example in the vicinity ofand for example just below a vessel roof.

The provision of a support structure to carry load for example inaccordance with the above described preferred embodiment means that atleast some of the load that might otherwise be carried by the walls ofthe vessel modules defining the active volume is carried instead as atensile load in the tensile slung members and then through the topsupport structure, and into the column perimeter wall structure as avertical compressive load. In addition to this arrangement allowing theload bearing capability of the overall structure to be concentrated inthe perimeter wall(s) and allowing the construction, all other thingsbeing equal, of potentially larger columns, it also offers furtherflexibility as regards loading conditions. For example, a staticpre-load may be applied to the overall structure. For example, apre-stressing load may be applied prior to or subsequent to theinclusion of packing material. For example, the sling members may bepre-tensioned.

In a possible embodiment, a column may be divided into plural flowzones.

This offers the possibility that the different vertical zones so definedby the modules may be used in different ways for different flowrequirements.

For example at a time of reduced flow only some of the modules might beused.

A further possible advantage of a modular structure follows from thefact that a column is readily divided into plural flow zones which arefluidly separate in that separate modules or groups of modules areadapted to serve in use as separate flow zones.

Additionally or alternatively for the same reason, a non-modular vesselmay be subdivided or a vessel column module may be further subdivided byinternal partition walls. Partition wall structures may be providedextending vertically along at least a part of the length of a vessel,and preferably the entire active length of the vessel, to partition thecolumn where they so extend into at least two zones which are fluidlyseparate. For example a non-modular vessel may be subdivided into innerand outer flow zones by a closed vertically extending internal wall. Theouter internal zone so defined may be further subdivided by further,radial, wall structures.

The vessel/vessel modules when assembled as the case may be define aperimeter shape for the active column volume which is conveniently aclosed simple curve such as a circle or an ellipse (that is, in such acase when vertical the column is a right cylinder) or, a closed simplepolygon (that is, in such a case when vertical the column is a rightprism). The perimeter structure defines a perimeter shape of the columnwhich may be of a similar shape to that of the perimeter shape of theactive column volume about which it extends or not.

References hereinbelow to a preferred column perimeter shape maytherefore be read either as references to a preferred perimeter shape ofthe active volume made up of the vessel/vessel modules when assembled asthe case may be or as references to the preferred perimeter shape of theperimeter structure.

In a particular embodiment a polygonal shape is preferred. Thus, inaccordance with the embodiment a column structure for the containment ofhigh surface-area packing and absorbent liquid reagent for the removalof a target gas from a gas stream comprises an elongate prismaticstructure having plural planar generally vertical perimeter wallstogether defining a closed simple polygonal perimeter. Although theshape may be square or rectangular, it is preferably one thatapproximates more closely to circular, and is for example one whereinthe internal angle between each wall making up the polygonal perimeteris at least 120° and less than 180°.

The distinct shape of the particular embodiment combines some of theadvantages of both principal prior art shapes, cylindrical andrectangular.

It approximates more closely to a cylindrical structure than arectangular column or vessel does. Thus, a polygonal prismatic columnarstructure in accordance with the preferred embodiment retains more ofthe inherent stiffness advantages of a cylindrical column, by its moreclose structural approximation to a cylindrical column, than is the casewith a rectangular vessel. In particular, the stiffness for a unit areais better than that for a rectangular column, with consequent advantagesfor the stability of the structure when packed, and for the stability ofplatform supports for the packing material.

The potential is offered for a greater structural size (that is, agreater surface area, and hence a greater volume per unit height) for anotherwise common range of structural parameters than would be the casewith a rectangular structure.

However, some of the practical drawbacks of the cylindrical column arereduced or eliminated. Individual vessel sections may be fabricated asand chipped as flat sheet structures. The sections themselves do notneed to have a curved structure. In a preferred case of modular vesselassembly, no module has a curved wall. Thus, the practical constraintsin this regard with respect to fabrication and shipping which havetended to limit the practical sizes of cylindrical, vessels to about 6 mhave been reduced. The design and installation of sealing edgesnecessary for tray operation may also be simplified.

A column/vessel structured in accordance with the shape of theparticular embodiment obviates some of the disadvantages of both priorart designs, cylindrical and rectangular, which tend to impose vesselsize constraints for a column/containment vessel. Moreover, thepolygonal shape works particularly well in conjunction with the tensileslung arrangement of the preferred embodiment above described.

In accordance with the preferred embodiment, the column is polygonal incross section with parallel walls defining a closed simple polygonalperimeter. The preferred shape is determined by structuralconsiderations, and for example by a desire to approximate more closelyto a cylindrical column. For example, the polygonal structure preferablycomprises a cyclic polygon (that is, the vertices define a circumscribedcircle), and is preferably a regular polygon (that is, equiangular andequilateral). An even number of sides is likely to be preferred, and inparticular a polygon which provides paired opposite parallel sides.

Although the column has planar sides, the internal angles at thevertices of the polygon defined by each side are preferably at least120°, and consequently the vessel has at least six sides. The totalnumber of sides is likely to be a compromise between a minimum numberbelow which a reasonable approximation to cylindrical structure is lostand a maximum number which reflects a desire to minimize complexity ofassembly. A vessel with 12 to 20 sides will typically be preferred formost applications.

Prior art vessels have typically been provided with a dished or domedwall and/or base to complete the closure. The top and/or base of thepresent column may comprise a partly pyramidal structure. In particular,the top and/or base may comprise a planar wall structure in which wallsections making up the top and/or base extend from the respectiveperimeter walls of the column. Again, such structures are easier tomanufacture, for example on a modular basis, and to transport forassembly in situ.

The column of the present invention is adapted for vertical operation,and for example adapted for the liquid to flow downwards from an inletnear the top and for the gas to be circulated counterwise upwards froman inlet near the bottom.

It is a particular advantage of the present invention that larger sizedcolumn structures, and in particular column structures with a largertransverse extent and thus a larger volume per unit height, can beconstructed more easily. In the preferred case, the vessel is sostructured as to have a minimum dimension in a transverse directionwhich is at least 10 m and more preferably at least 15 m to 30 m ormore.

As discussed above, the throughput rates required for large thermalpower plants would suggest a requirement for cylindrical columnstructures with a diameter of 18 m to 24 m or more. A column structurein accordance with the present invention preferably has comparabletransverse dimensions. In the case where the column structure comprisesa cyclic polygon such as a regular polygon, it can be defined by acircumscribed circle having such a diameter.

This can be contrasted with present vessels, where structural,fabrication and transport considerations applicable to conventionalpractical materials such as structural steel have been held to limit thepractical dimensions of a cylindrical vessel to a diameter of around 6m, and to limit the practical shortest direction of a rectangular vesselto a similar 6 m.

The envisaged use of a column structure in accordance with the inventionis as a packed tower comprising high surface area packing material andabsorbent liquid reagent for the removal of a target gas from a gasstream.

In a more complete embodiment of the invention there is provided such apacked tower absorber column comprising a column structure as abovedescribed with packing material in situ.

In a particular preferred case the column structure comprises aplurality of support platform structures carrying packing material in aplurality of column sections, including at least one and preferably aplurality of absorbent liquid reagent stages and at least one washingstage.

Preferably, the packing material is a structured packing material. Thestructured packing material provides a high surface area structure toprovide a high gas/liquid contact area per unit volume for high masstransfer, and may be of suitable familiar form, in particular providingplural arrays of thin corrugated metal sheet. The precise nature of thepacking material is not pertinent to the invention, which is intended tobe used with known packing materials and known absorbent chemistries,but which will also support new packing materials and chemistries asthey are developed.

In a more complete embodiment, the internal volume of the columnpreferably further comprises, typically for example disposed at the topof each structured packing section, one or more of a collectorstructures, a distributor structure, and a bed limiter in familiarmanner. The column may further comprise in a washing stage a demisterstructure. All the foregoing will be of familiar design scaled up asapplicable to the larger columns made possible in the present invention.

The column preferably further comprises a means to supply absorbentsolution through one or more inlets in the vicinity of the top of thecolumn.

In the preferred case the modular structure defines a plurality offluidly distinct process volumes in two dimensional array about the areaof the column. A means to supply absorbent solution to and through oneor more inlets in the vicinity of the top of the column preferablycomprises a means to distribute solution between each process volume. Ina possible embodiment, plural supply pipes extend across the top of theprocess volumes. Each supply pipe may supply a plurality of processvolumes for examples arranged in a row. Such a supply pipe maycorrespondingly have a plurality of supply apertures. Plural supplypipes may be supplied with absorbent liquid reagent from a common supplymanifold, for example located at or about a part of the perimeter of thecolumn.

The column preferably further comprises a means to supply gas to betreated through one or more inlets in the vicinity of the base of thecolumn.

In the preferred case to accommodate a modular structure defining pluralprocess volumes the column, the means to supply a gas to be treated toone or more inlets in the vicinity of the base of the column similarlycomprises a means to distribute the gas to be treated between the pluralprocess volumes.

As above described, the column structure defines one or more secondaryfluid volumes which are fluidly isolated from the process volumes, forexample in that the outer wall surfaces of the vessel structure orassembly and the inner wall surfaces of the perimeter structure togetherdefine one or more secondary fluid volumes which are fluidly isolatedfrom the process volumes. The column preferably further comprises ameans to supply gas to the secondary volume in a manner which maintainsin a secondary volume a relatively inert atmosphere, in particular anatmosphere which does not comprise absorbent liquid reagent. The gassupplied to the secondary volume may be a secondary gas, or may be a drysupply of the gas to be treated.

In the preferred application the column is a CO₂ wet scrubber, and thesolution may comprise one or more aqueous amines, for example includingbut not limited to monoethanolamines or methyl-diethanol-amines.

In the preferred application a column is provided for use in a scrubbercolumn for flue gases and is provided with a flue inlet towards thebottom of the column.

In accordance with the invention in a further aspect a method ofassembly of a column structure for the containment of high surface areapacking and absorbent liquid reagent for the removal of a target gasfrom a gas stream comprises the steps of

providing one or more vessels having an elongate upright wall structureto define and fluidly enclose an absorption process volume for thecontainment of high surface area packing and for the countercurrent flowof absorbent liquid reagent and target gas in use;

providing a column perimeter structure comprising an elongate uprightwall structure;

surroundingly enclosing the vessel(s) within the column perimeterstructure, in such assembled manner that an inner wall of the elongateupright wall structure and an outer wall of a vessel cooperably defineand fluidly enclose at least one secondary fluid volume fluidly isolatedfrom the absorption process volume(s) and preferably in such assembledmanner that a major part of the load of the assembled column structureis carried by the column perimeter structure.

In a possible embodiment the method comprises providing a plurality ofvessel column modules each having an elongate upright wall structure,and arranging the vessel modules together alongside one another in twodimensional array within the column perimeter structure.

In a possible embodiment each column module comprises plural sub-modulesand the method comprises:

assembling multiple such pluralities of sub-modules together in elongatearray to form multiple elongate vessel column modules;

arranging the vessel column modules vertically together alongside oneanother in two dimensional array to constitute collectively said columnstructure such that the vessel modules collectively comprise a columnarvessel assembly as above.

Particularly preferably, each column module is assembled by the assemblyof each of its plurality of constituent sub-modules successively fromthe top downwards.

In a possible embodiment the method comprises:

providing a column top support structure;

supporting each vessel/column module mechanically in the vicinity of theupper part of a column structure so assembled via the top supportstructure.

The module volumes collectively comprise an active absorption volume andthe active volume collectively so defined is used for the removal of atarget gas from a gas stream by means of an absorbent liquid reagent,and the packing layer provides a high surface area for mass transport.

The vessel(s) or vessel modules are arranged with the column perimeterstructure in such assembled manner that an inner wall of the elongateupright wall structure and an outer wall of a vessel cooperably defineand fluidly enclose at least one secondary fluid volume fluidly isolatedfrom the absorption process volume(s) defined by the inner wall(s) ofthe vessel(s) or vessel modules. Preferably, the vessel(s) or vesselmodules are disposed within the volume defined by the column perimeterstructure in such a manner that the process volume(s) within each vesselor vessel module are kept fluidly separate from the one or moresecondary volumes defined within the volume defined by the columnperimeter structure but outside the process volume defined by thevessel(s). For example the vessel(s) or vessel modules are assembledsuch that a secondary volume comprises a space between the wall(s) of avessel module and each adjacent module and/or a space between thewall(s) of a vessel or vessel module and the wall(s) of the perimeterstructure. The assembly method may further comprise providing fluidseals appropriately located in the spaces between the said walls tofluidly separate the process volume(s) from the secondary volume(s).

Preferably, the vessel(s) or vessel column modules are assembled to besupported by the column perimeter structure, for example via a supportstructure in an upper part thereof.

Preferably the column perimeter structure is provided with:

a top support structure extending inwardly from the perimeter of avessel towards the top thereof; and

slung tensile members attached to the top support structure;

and an internal column structure, for example selected from a transverseplatform support structure for a high surface area packing material, avessel or a vessel module, is assembled to be supported by the slungtensile members.

For example at least the vessel(s) or vessel modules are assembled to besupported by the slung tensile members.

The method of this aspect is in particular a method of assembly of acolumn in accordance with the first aspect of the invention. Otherpreferred features of the method will be understood by analogy.

In accordance with the invention in a further aspect a method ofprocessing of a gas phase to effect separation of a component of the gasphase by absorption into a liquid phase comprises:

providing a column in accordance with the first aspect of the inventionor assembled in accordance with the second aspect of the invention, inparticular preferably packed with high surface area material packingsuch as structured packing;

causing the gas phase to flow through the column;

causing a liquid phase comprising an absorbent reagent to flowcountercurrently through the column.

As a result, the liquid and gas phases are countercurrently brought intocontact to cause the target component of the gas phase to be absorbedinto the liquid phase in familiar manner.

Preferably the column is disposed generally vertically, the gas phase isintroduced towards the lower part of the column and caused to flowupwardly, and the liquid phase is introduced towards the lower part ofthe column and caused to flow downwardly.

In a preferred refinement of the method, the liquid phase and gas phaseto be processed are introduced to the active absorption volume, and arelatively less reactive atmosphere is maintained within the columnoutside the active absorption volume for example at least in that it isnot exposed to the liquid phase. In particular this is done in that thevessel(s) making up an active absorption volume are arranged such thatthe column outside the active absorption volume defines a secondaryvolume that is kept fluidly isolated from the active absorption volumeand into which liquid phase is not introduced. The process gas phasewithout the liquid phase or another relatively inert gas phase may beintroduced to the secondary volume, for example prior to introduction ofthe liquid phase to the process volume and/or at a degree ofoverpressure to limit leakage of liquid phase into the secondary volumeand so to tend to maintain a relatively less chemically reactiveatmosphere therein.

In a convenient case, the column comprises a perimeter structure and thesecondary volume comprises the column volume within the perimeterstructure but outside the primary absorption volume. The method in thiscase comprises introducing the liquid phase and gas phase to beprocessed to the primary absorption volume and introducing the processgas phase without the liquid phase or another relatively inert gas phaseto the secondary volume.

In the preferred case, the column comprises a plurality of vessel columnmodules each defining a process volume, the modules being so assembledas to together comprise the primary active volume, and the secondaryvolume comprises the column volume outside the process volumes togethercomprising the primary active volume that is kept fluidly isolatedtherefrom. The method in this case comprises introducing the liquidphase and gas phase to be processed to the process volumes of theseveral modules, and maintaining a relatively less chemically reactiveatmosphere in the secondary volume, at least in that the secondaryvolume is kept fluidly isolated from the active absorption volume andliquid phase is not introduced into it.

The method is in particular a method of operation of a column inaccordance with the first aspect of the invention. Other preferredfeatures of the method will thus be understood by analogy.

The invention will now be described by way of example only withreference to FIGS. 1 to 6 of the accompanying drawings, wherein:

FIG. 1 is a longitudinal cross section through a column structureembodying the principles of the invention;

FIG. 2 is a longitudinal cross section through a vessel module making upthe column structure of FIG. 1;

FIG. 3 illustrates in enlarged view a slung tensile member of theembodiment of FIG. 2;

FIGS. 3 a to 3 c illustrate baskets for containing high surface areapacking;

FIG. 4 illustrates in plan view a floor support framework for a platformlevel in the column structure of FIG. 1;

FIG. 4 a illustrates sections through the possible suspension structure;

FIG. 4 b shows a developed view from below of a suspension roof;

FIG. 4 illustrates in plan view a possible suspension structure;

FIG. 5 illustrates in top plan view an example arrangement of modulesand an example system for the distribution of solution into each module;

FIG. 6 illustrates in top plan view an alternative arrangement ofmodules.

FIG. 1 illustrates a vertically oriented column to serve as a flue gasscrubber or absorber for post-combustion capture of CO₂ from the fluegas of a thermal power plant using a carbonaceous fuel source. Thecolumn of FIG. 1 embodies the structural principles of the presentinvention as illustrated in more detail in the other figures.

The absorber column shown as an embodiment of the invention is based ona 24.7 m circular column absorber as might be required for single streampost-combustion CO₂ capture from an 800 MW plant. The column 21comprises an outer containment vessel having a vertical cylindrical wallstructure 22. The vessel defines a gas inlet 23 which in the example isan inlet for flue gases (which may be direct or partly pre-processed)from a thermal power plant, and a gas outlet 31 which will vent fluegases to atmosphere or pass for further processing having been scrubbed.The flue gases circulate from bottom to top, and absorbent solution isintroduced towards the top of the column to circulate in the counterwisedirection in familiar manner.

The reactive volumes within the internal columns are fluidly isolatedfrom secondary volume(s) defined outside the internal columns but withinthe perimeter wall 22. The insets in FIG. 1 illustrates how this is doneby provision of a seal. The upper inset shows detail of a typical sealat the top end of the internal columns. The lower inset shows detail ofa typical seal at the bottom of the internal columns. With these sealsin place any flue gas leakage from the secondary volume will be throughthe gap between protective angle and the column or through any otherleakage due to construction faults of internal walls and the negativepressure within the column. Therefore the outer column is protected fromthe reactive fluids in the internal columns.

For modularization purposes the column is in the example embodimentsubdivided into 32 internal packed vertically extending column modules,as can be seen in more detail in FIG. 5. In the representation in FIG. 1six such vessel column modules can be seen in cross section across thecolumn. It is within the process volumes defined by the vessel columnmodules that the solution is introduced towards the top of the column tocirculate in the counterwise direction to the flue gas, and it is withinthe process volumes defined by the vessel column modules that absorptiontakes place.

An example vessel column module is shown in longitudinal cross sectionin FIG. 2. The column module has a polygonal vessel wall 15 containingstructured packing to provide the necessary surface area for contactbetween absorbent solution introduced from the top and flue gasescirculating upwards. In the embodiment, plural column zones comprisingseparate sections of structured packing are shown, being successivestructured packing layers, and additionally two wash sections ofstructured packing layers at the top. Such multiple stages andstructures will be generally familiar to the person skilled in the artfrom generally equivalent structures found in prior art single vesselcolumns.

The column module vessel walls 15 define the reactive volume in whichabsorption takes place and need to resist the harsh environmentattributable to the absorbent liquid. However, in the illustratedembodiment, most of the load is carried by the wall structure 22. Thedesign and material selection for the vessel modules keeps this in mind.Suitable materials for the vessel module walls 15 include: stainlesssteel, for example grade 316, 3 mm thick; and reinforced plastic, forexample Fortron 1140L4, 10 mm thick. The embodiment in FIG. 2 is anexample of the latter.

Structured packing is carried on support grids 1, 3. All support gridsare supported by continuous angle 13. A support grid is constructedusing flat plates. Wall restraints 4 are provided.

The structured packing is divided into three main vertical sections forabsorption and two wash sections above, each provided with a liquiddistributor or redistributor 5 at the top of the section and a liquidcollector 7 at the bottom in generally familiar manner. These may befixed in position and sealed prior to installation of the packing. Inthe figure these are shown spaced apart by the temporary frameworkelements 6. These can be wooden and removed after site welding.

For further modularization purposes each vertically extending columnmodule is further divided into plural successively vertically arrayedsub-modules.

In the embodiment each sub-module may comprise a basket defining acontainment means for a discrete portion of high surface area packingand carrying the same in the assembled column. Basket alignment platesare provided up the column. There are nine baskets in each packedmodule. These baskets are designed to be packed and fabricated inmanufacturing bays from the top down progressively with the otherequipment shown in FIG. 2. The purpose of this is to minimizeconstruction time on site.

The height of a basket is determined based on the feasibility oftransportation and may be around 4500 mm. However, the height will beinfluenced also by the dimensions of other equipment in the module andby the location of suitable site welds.

The width, length and shape of a basket are determined based on itslocation, and on the dimensions and shape of the module in which itlocates and of its position therein in particular. Again, typically eachof these dimensions may be limited to a maximum of around 4500 mm.

The operational process is familiar. A suitable absorbent liquid suchas, in a familiar chemistry, amine dissolved in water, is used. This issupplied by the supply pipes 9 to the process volume of each module. Thegas to be scrubbed, in the embodiment flue gas from a thermal powerplant, is introduced into the lower part of the column via the gas inlet23 and fresh absorbent solution is introduced from towards the top ofthe column into each vessel module. The absorbent liquid runs downthrough the structured packing as the CO₂ rich flue gas passes upthrough it.

CO₂ in the flue gas will be absorbed by the amine solution by formationof weak chemical bonds. Thus, as is familiar, the amine solution isenriched with CO₂ as it travels down the column and CO₂ is removed fromthe flue gas as it travels up the column.

The gas continues into the washing stages where it is washed by awashing liquid circulated via the supply pipes 11 and return pipes 10.

When the flue gas reaches the top of the column it is vented to theatmosphere or passed for further processing via the outlet 31, at whichpoint a large proportion of the CO₂ has been removed.

CO₂ enriched amine solution passes through into the lower volume 32 tobe discharged via outlet 35. The solution is passed on to suitableapparatus for recovery of the CO₂. Typically this process involvesregenerative heating of the amine solution. At higher temperatures thesolution will release the absorbed CO₂ and be regenerated for reuse inthe absorption column. The released CO₂ is collected for sequestration.The principles of chemistry are thus familiar.

The illustrated embodiment differs from prior art cylindrical columns inthree ways in particular, which offer the potential for it to haveoptimized load bearing capability and facilitate its assembly in situ.

First, the column in the embodiment is of a modular structure havingplural column modules in horizontal array with individual column moduleshousing the reactive volumes and the outer shell providing much of thestructural support. This simplifies assembly and offers flexibility ofsize.

This aspect of the modular structure can be seen in greater detail inFIGS. 5 and 6 and is discussed below.

Second, the column modules are supported by elongate tensile members 12slung from the roof 34. Additionally or alternatively tensile membersmay be slung from a support deck inside the roof. This support deck ifthen fixed to the perimeter wall structure 22. In either case, theadditional support structure transfers the load in a more stable wayinto and directly down through the perimeter wall structure 22.

The sling system 12 is shown in greater detail in FIG. 3. It comprises alug and plate beam 12 a, slung rod with spade end 12 b and invertedsupport angles 12 c welded to the walls.

Third the column modules in the embodiment are assembled from multiplevertically arrayed baskets. These may be slung successively from the topdown having been pre-fabricated off-site.

FIGS. 3 a to 3 c illustrate baskets defining a containment means for adiscrete portion of high surface area packing and carrying the same inthe assembled column. FIGS. 3 a are horizontal cross-sections baskets ofeach of the three column shapes illustrated in FIGS. 5 and 6 andrespectively labelled thereon as type 1, type 2, type 3. FIG. 3 b is aside wall of a basket in side elevation. FIG. 3 c is a floor detail forthe basket of square cross-section shape.

The modular structure of the embodiment is not a requirement of theinvention but is a convenient mechanical arrangement by means of whichthe feature of the invention of providing secondary volume(s) fluidlyisolated from the active volumes can be achieved.

The modular arrangement can be exploited in this way by fluidlyisolating the volumes within the vessel modules from secondary volume(s)defined outside the vessel modules but within the perimeter wall 22. Theinsets in FIG. 1 illustrates how this is done by provision of a seal.The volumes within the vessel modules comprise reactive volumes in whicha mixture of gas and absorbent solution is supplied and absorption takesplace. The volume outside the vessel modules but within the perimeterwall is a fluidly separate secondary volume. This secondary volume neednot have the harsh environment of the absorbent solution, but mayinstead be supplied with a dry relatively more inert atmosphere. Thismodular arrangement is an effective may of achieving this, but anarrangement which provides a similarly isolated single non-modularvessel defining a process volume can readily be envisaged.

In all such cases the perimeter wall 22 may thus be designed for noliquid contact. It need not have the chemical resistance required of awall of the process volume. It may be designed for its mechanicalsupport role. This is achieved for example in the embodiment by means ofthe following: all interconnecting welds between walls and baskets areseal welds;

all gaps between seal plates are eliminated;

all bolts and washers are seal welded to the walls;

the protective angle shown in the enlarged view in FIG. 1 iscircumferentially continuous;

the absorber is pressurized prior to introduction of liquid into themodules.

The perimeter wall may then be constructed from material with itsmechanical support role paramount. For example it may be concrete orcarbon steel without any lining requirement.

The perimeter wall may additionally have structural modificationsenhancing its mechanical support role. For example, in the embodiment,it carries the vessel modules via slung roof supports, and supports thesuspension decks directly on the wall.

From a process control view point the outer enclosure is only requiredto provide a secondary fluid volume: (a) from ground up to the bottom ofthe module vessels where vessels must be sealed from gas leakage to theoutside atmosphere; (b) from top seal where the “clean” gas is requiredto be vent to atmosphere. From a structural point of view the perimeterstructure needs to transmit load from the point at which columnstructures are supported (for example, from the suspension deck) butneed not form an enclosing perimeter for a secondary volume. Thus loadmay be transmitted to the ground by structural elements of the perimeterstructure, which could be totally independent or integrated with the topand bottom enclosures above described. In the embodiment a single outerwall structure 22 is provided in conjunction with suitable seals toperform both roles, but this is not a requirement of the invention.

A vessel wall 15 may likewise be optimized for its role as a containmentvessel for the process volume with the required chemical resistance butwith reduced contribution to the carrying of the structural load. Largerand more flexible column structures can be made possible.

FIG. 4 illustrates in plan view a possible platform structure.

FIG. 4 a illustrates sections through a possible platform suspensionstructure showing the suspension of the platform structure of FIG. 4from the conical outer shell roof structure. Sections are shown from thetop respectively through (as marked in FIG. 4) section J-J (K-K) issimilar with members interconnected in between; section L-L (M-M) issimilar with members interconnected in between and outer shell omitted;section N-N (P-P) is similar with members interconnected in between.

FIG. 4 b shows a developed view from the underside of the top cone rooffrom which the platform structure of FIG. 4 is suspended.

A possible design of a typical absorbent liquid supply system is shownin plan view in FIG. 5. A common source pipe 41 feeds a manifold 43 incommunication with a series of supply pipes 45 extending into the columnat an appropriate absorbent liquid supply level. The supply pipes 45 arecontinuous and sealed around where they pass through the walls forexample by a suitable washer. Outlets 47 are provided to supply eachvolume defined by each vessel module. The pipes 45 have progressivelyreducing diameter to facilitate even supply.

FIG. 5 also illustrates an example arrangement of and shapes of vesselmodules. In FIG. 5 the modules define an inner zone in which moduleswith planar walls and square transverse section are in a square 4×4array and a perimeter zone in which each module has planar walls whereadapted to sit in the assembled structure adjacent an inner zone moduleand curved walls adapted to sit in the assembled structure adjacent acorrespondingly curved perimeter structure. The modules are assembled intessellating manner such that the curved walls of the perimeter zonemodules give a circular perimeter to the vessel assembly, which thusforms a cylindrical column.

It can be seen that this minimizes the range of modules required. Eachmodule in the inner zone is identical (type 3) and only four moduledesigns respectively being mirror image pairs (type 1 a, b and type 2 a,b) are required in the perimeter zone. This simplifies the assemblyprocess.

FIG. 6 illustrates an alternative arrangement with alternative moduledesign to produce a vessel assembly with a polygonal (in the example aregular hexadecagonal) perimeter. Again each module in the inner zone isidentical with square perimeter (type 3). Again the perimeter zonemodules are of four designs respectively being mirror image pairs (type1 a, b and type 2 a, b), but in this case the perimeter zone modules aresuitable shaped irregular polygonal prisms. The modules are assembled intessellating manner to create the hexadecagonal vessel assembly.

The perimeter wall structure is in the example cylindrical, but mayalternatively also be polygonal.

1. A column structure for the containment of high surface area packingand absorbent liquid reagent for the removal of a target gas from a gasstream comprising at least one vessel having an elongate upright wallstructure to define and fluidly enclose an absorption process volume forthe containment of high surface area packing and for the countercurrentflow of absorbent liquid reagent and target gas in use; and a columnperimeter structure comprising an elongate upright wall structure havinga continuous and closed perimeter disposed around the at least onevessel in such manner that an inner wall of the elongate upright wallstructure and an outer wall of a vessel cooperably define and fluidlyenclose at least one secondary fluid volume fluidly isolated from theabsorption process volume(s).
 2. A column structure in accordance withclaim 1 wherein the column perimeter structure is so arranged withrespect to the vessel(s) as to create one or more secondary fluidvolumes defined at least by the outer wall surface(s) of the wall(s) ofthe vessel(s) and the inner wall surface(s) of the perimeter structure,wherein a primary volume comprising the process volume defined by eachvessel is fluidly separate from said secondary fluid volumes.
 3. Acolumn structure in accordance with claim 2 comprising a plurality ofvessels and wherein the secondary fluid volume additionally comprisesspace between the wall(s) of a vessel module and an adjacent module. 4.A column structure in accordance with claim 1 wherein absorbent liquidsupply means are provided to supply absorbent liquid reagent only to theprocess volume(s).
 5. A column structure in accordance with claim 4comprising means to supply a gas to be processed to the processvolume(s) to flow counter-currently with the absorbent liquid reagent,and to supply a gas to the secondary volumes to create a relatively lessreactive atmosphere.
 6. A column structure in accordance with claim 1wherein the wherein the column perimeter structure is adapted to carry amajor part of the structural load of the column structure.
 7. A columnstructure in accordance with claim 1 comprising a plurality of vesselmodules each having an elongate upright wall structure, the modulesbeing disposed together alongside one another in two dimensional arrayto constitute collectively the column structure.
 8. A column structurein accordance with claim 7 wherein each vessel module has an elongateupright wall structure defining a perimeter that surrounds a processvolume within the vessel module.
 9. A column structure in accordancewith claim 8 wherein the vessel module perimeter comprises a closedsimple polygon or closed simple curve or combination of the same.
 10. Acolumn structure in accordance with claim 7 wherein all vessel modulewalls that are entirely internal to the vessel assembly are planar. 11.A column structure in accordance with claim 7 wherein all vessel modulesthat are entirely internal to the vessel assembly have a square orrectangular perimeter shape.
 12. A column structure in accordance withclaim 7 wherein all vessel modules that are entirely internal to thevessel assembly are of identical shape and size.
 13. A column structurein accordance with claim 7 wherein the vessel modules are arranged insuch manner that adjacent vessel walls of adjacent vessel modules extendsubstantially parallel to one another when the vessel modules arelocated in position.
 14. A column structure in accordance with claim 13wherein the vessel walls are generally evenly spaced when the vesselmodules are located in position.
 15. A column structure in accordancewith claim 1 wherein the column perimeter structure comprises anelongate upright wall structure defining a perimeter comprising a closedsimple polygon or closed simple curve.
 16. A column structure inaccordance with claim 1 wherein the column perimeter structureadditionally comprises a roof closure or partial closure, wherein theroof closure or partial closure or additional means disposed andsupported within a roof volume it defines are adapted to contribute to acolumn load bearing capacity of the perimeter wall structure.
 17. Acolumn structure in accordance with claim 1 wherein the column perimeterstructure is provided with: a top support structure extending inwardlyfrom the perimeter of a vessel towards the top thereof; and tensilemembers attached to the top support structure and extending downwardlyto support at least one internal column structure selected from: atransverse platform support structure for a high surface area packingmaterial and/or a vessel or vessel module.
 18. A column structure inaccordance with claim 1 having a polygonal perimeter shape wherein theinternal angle between each wall making up the polygonal perimeter is atleast 120° and less than 180° and thus comprising a prismatic columnarstructure.
 19. A column structure in accordance with claim 1 having acircular perimeter shape and thus comprising a cylindrical columnarstructure.
 20. A method of assembly of a column structure for thecontainment of high surface area packing and absorbent liquid reagentfor the removal of a target gas from a gas stream comprises the steps ofproviding one or more vessels having an elongate upright wall structureto define and fluidly enclose an absorption process volume for thecontainment of high surface area packing and for the countercurrent flowof absorbent liquid reagent and target gas in use; providing a columnperimeter structure comprising an elongate upright wall structure;surroundingly enclosing the vessel(s) within the column perimeterstructure, in such assembled manner that an inner wall of the elongateupright wall structure and an outer wall of a vessel cooperably defineand fluidly enclose at least one secondary fluid volume fluidly isolatedfrom the absorption process volume(s).
 21. A method in accordance withclaim 20 wherein the column perimeter structure and vessel modules areso assembled that a major part of the load of the assembled columnstructure is carried by the column perimeter structure.
 22. A method inaccordance with claim 21 wherein the column perimeter structure isprovided with: a top support structure extending inwardly from theperimeter of a vessel towards the top thereof; and tensile membersattached to the top support structure; and the vessel(s) are assembledto be supported by the tensile members.
 23. A method in accordance withclaim 20 wherein the vessel(s) are disposed within the volume defined bythe column perimeter structure in such a manner that a primary volumecomprising the process volume(s) defined by each vessel is kept fluidlyseparate from one or more secondary volumes defined within the volumedefined by the column perimeter structure but outside the process volumedefined by each vessel.
 24. A method in accordance with claim 23 whereinthe vessel(s) are assembled such that a secondary volume comprises aspace between the wall(s) of a vessel and wall(s) of the perimeterstructure.
 25. A method in accordance with claim 24 further comprisingthe step of providing fluid seals appropriately located in the spacesbetween the said walls to fluidly separate the process volumes from thesecondary volume(s).
 26. A method in accordance with claim 20comprising: providing a plurality of vessel modules each having anelongate upright wall structure, and arranging the vessel modulestogether alongside one another in two dimensional array to constitutecollectively said column structure such that the vessel modulescollectively comprise a columnar vessel assembly.
 27. A method ofprocessing of a gas phase to effect separation of a component of the gasphase by absorption into a liquid phase comprises: providing a column inaccordance with claim 1 providing high surface area packing material inthe column; causing the gas phase to flow through the column; causing aliquid phase comprising absorbent reagent to flow countercurrentlythrough the column.
 28. A method in accordance with claim 27 wherein thegas phase is introduced towards the lower part of the column and causedto flow upwardly, and the liquid phase is introduced towards the lowerpart of the column and caused to flow downwardly.
 29. A method inaccordance with claim 27 wherein a fluidly distinct active absorptionvolume is defined within the column, the liquid phase and gas phase tobe processed are introduced to the active absorption volume, and arelatively less reactive atmosphere is maintained within the columnoutside the active absorption volume.
 30. A method in accordance withclaim 29 wherein the vessel(s) are assembled such that a secondaryvolume comprises a space between the wall(s) of a vessel and wall(s) ofthe perimeter structure the liquid phase and gas phase to be processedare introduced to the vessels, and a relatively less reactive atmosphereis maintained within the space between the wall(s) of a vessel andwall(s) of the perimeter structure.
 31. A method in accordance withclaim 29 wherein the process gas phase without the liquid phase oranother relatively inert gas phase is introduced to the secondaryvolume.
 32. A method in accordance with claim 31 wherein the gas isintroduced to the secondary volume prior to introduction of the liquidphase to the process volume and/or at a degree of overpressure to limitleakage of liquid phase into the secondary volume and so to tend tomaintain a relatively less chemically reactive atmosphere therein.